[moij]

Here some data about my OB speakers and some questions.
Elements used are Fountek NeoCD3.5H, Scan-Speak 15M/4624G00 in MTM alignment on triangular baffle, Selenium WPU 1805-X on 30 cm deep U-frame. Mid and tweeter filter is passive, bass filter is active with baffle compensation EQ.
One image of speakers, NeoCD3.5H horns only installed:


Schematic of bass filter and EQ is:


Baffle compensation EQ curve is:


Comparison of baffle compensated and not compensated SPL in listening position:


Measured SPL of left speaker and decay (lowest blue line is 160 ms) in listening position:


Measured SPL of right speaker and decay (lowest blue line is 160 ms) in listening position:


THD of left speaker in nearfield, in not compensated range is power about 1 W:


And the question is: how to damp room modes on 21, 36 and 46 Hz seen on dacay images? Can EQ-ing out room modes give good results?
Basically room had non parallel ceiling and floor, REW measured EDT is 0.4 -0.1 s from 100 Hz to 20000 Hz, but more than 1 s in lower than 100  Hz range.
For illustration also REW spectrogram:

[JohnR]

Nice! How do you like those 15Ms? Been considering them...

With regard to the modes, do different positions have any effect?

[AJinFLA]

Well thought out and very nicely done

[moij]

Nice! How do you like those 15Ms? Been considering them...

With regard to the modes, do different positions have any effect?

I nearly like 15M/4624G00, only when all was ready, I find that to much mid with 18" bass speaker seamlessly,  the mid must be large, about 6"-8". Also then can  smaller panel be used and less panel(edge) reflection is get, now peaks in  500 Hz and 1500 Hz range are purely panel caused.

Modes are little different in left and right channels as you can see from images, 21 Hz is in both. It is logical as room is asymmetric.
But locations are best possible in meaning of mid and high frequencies and stage image.

[JohnR]

I nearly like 15M/4624G00, only when all was ready, I find that to much mid with 18" bass speaker seamlessly,  the mid must be large, about 6"-8". Also then can  smaller panel be used and less panel(edge) reflection is get, now peaks in  500 Hz and 1500 Hz range are purely panel caused.

Understood, thank you.

Modes are little different in left and right channels as you can see from images, 21 Hz is in both. It is logical as room is asymmetric.
But locations are best possible in meaning of mid and high frequencies and stage image.

I think perhaps the first thing to do then would be to do the measurement with both speakers running. You could use parametric EQ at eg 36 Hz which will ameliorate the effect although not remove the mode. However, it looks to me as though you have more boost than you need, can you adjust the analog EQ to reduce the amount of boost below say 40-50 Hz? (But this would depend on the measurement with both speakers.)

[moij]

I can use additional EQ but with EQ I only can compensate room gain but not damp room modes and get rid of long reverberation on 21, 36 and 46 Hz.

[JohnR]

Um, I am suggesting using less boost in your analog EQ. But first measure both speaker together and see what the decay times/modes are for them combined.

[moij]

I also made measurement when both speakers connected, no big differece. All bigger peaks where present from both.

[JohnR]

Well, I would be inclined to reduce the gain of the EQ down low say < 50-60 Hz. Or use a parametric to flatten it out. It won't remove the modes but it will make them less apparent. To damp the modes acoustically would be pretty challenging I think, I'd be interested to know if you are able to make progress with it. There are some vendors that sell resonant traps e.g. GIK have one tuned to about 40 Hz I think.

[moij]

I am looking advices how to make bass traps as DIY. I had plaster board walls and opposite side of wall is partly usable for trap, behind some walls is relatively big space, kind of attic or garret.

[JohnR]

Hi, the info and links in this article may be some help:

http://www.hifizine.com/2011/09/bass-integration-guide-part-2/

[moij]

Latest update to speakers is DSP, what now is taking care of all filtering, OB compensation and equalisation.
Left channel SPL is

As seen, room modes are still present.